Nuclear probes of an out-of-equilibrium plasma at the highest compression

• Published in: Physics letters. A 2019-07, Vol.383 (19), p.2285-2289
• Main Authors: Zhang, G., Huang, M., Bonasera, A., Ma, Y.G., Shen, B.F., Wang, H.W., Wang, W.P., Xu, J.C., Fan, G.T., Fu, H.J., Xue, H., Zheng, H., Liu, L.X., Zhang, S., Li, W.J., Cao, X.G., Deng, X.G., Li, X.Y., Liu, Y.C., Yu, Y., Zhang, Y., Fu, C.B., Zhang, X.P.
• Format: Article
• Language: English
• Subjects: High-energy-density plasma; Inertia confinement fusion; Laser plasma; Nuclear astrophysics; Physics
• ISSN: 0375-9601; 1873-2429
• DOI: 10.1016/j.physleta.2019.04.048

We report the highest compression reached in laboratory plasmas using eight laser beams, E≈laser12 kJ, τlaser=2 ns in third harmonic on a CD2 target at the ShenGuang-II Upgrade (SGII-Up) facility in Shanghai, China. We estimate the deuterium density ρD=2.0±0.9 kg/cm3, and the average kinetic energy of the plasma ions less than 1 keV. The highest reached areal density ΛρD=4.8±1.5 g/cm2 was obtained from the measured ratio of the sequential ternary fusion reactions (dd→t+p and t+d→α+n) and the two body reaction fusions (dd→3He+n). At such high densities, sequential ternary and also quaternary nuclear reactions become important as well (i.e. n(14.1 MeV)+12C → n'+12C* etc.) resulting in a shift of the neutron (and proton) kinetic energies from their birth values. The Down Scatter Ratio (DSR-quaternary nuclear reactions) method, i.e. the ratio of the 10-12 MeV neutrons divided by the total number of 14.1 MeV neutrons produced, confirms the high densities reported above. The estimated lifetime of the highly compressed plasma is 52 ± 9 ps, much smaller than the lasers pulse duration. •A very high compression stage can be reached by ten kilo joules nanosecond lasers hitting on a planar CD2 target.•The ratio between the secondary neutron yield and the primary one provides a robust probe for the density of the plasma.•Important non-equilibrium effects might change substantially the plasma dynamics resulting in an ‘effective temperature’ less than 1 keV.